Shinya Koga

Conducting Pathways in North Temperate Deciduous Broadleaved Trees

The interspecific variation of dye ascent in the stems of 44 broadleaved deciduous species growing in Japan was studied using freeze-dried samples after dye injection. The dye ascending pattern differed both within and between ring-porous and diffuse-porous species. In large earlywood vessels of all ring-porous species, the dye ascended only in the outermost annual ring, and the inner annual rings had lost their water transport function. The dye ascending pattern within the inner annual rings in the ring-porous species was categorized into three types: i) the dye ascended both in the many latewood vessels throughout the latewood and small earlywood vessels; ii) the dye ascended in the many vessels throughout the latewood; and iii) the dye ascended mainly in the late latewood vessels. In diffuse-porous species, the dye ascending pattern within the annual rings also was categorized into three types: i) the dye ascended throughout the annual rings; ii) the dye ascended mainly in the earlywood vessels; and iii) the dye ascended mainly in the latewood vessels. Xylem water distribution was also examined by cryo-SEM in three ring-porous and three diffuse-porous species that had different dye ascending patterns. The water distribution pattern within annual rings was correlated with the dye ascending pattern except for one diffuseporous species (Salix gracilistyla). In this case, water was distributed in the whole region of the annual rings although dye was mainly distributed in the earlywood. These results showed that the functional area of water transport within annual rings differed among ring-porous species and diffuse-porous species.

Xylem water-conducting patterns of 34 broadleaved evergreen trees in southern Japan

A dye injection method was used to elucidate the xylem water-conducting pathways of 34 broadleaved evergreen trees growing in southern Japan: two semi-ring-porous, 26 diffuse-porous, five radial-porous and one non-vessel species. The large earlywood vessels in semi-ring-porous species have a water transport function in only the outermost annual ring, as in deciduous ring-porous species. On the other hand, the small vessels in semi-ring-porous species maintain the water transport function in many outer annual rings. For the other xylem-type species, the many vessels in many outer annual rings have a water transport function. In diffuse-porous species, we categorized the water-conducting pattern within the annual rings into two types: d1 type, where water travels through vessels in the whole region; and d2 type, where water travels mainly through the earlywood vessels. The pattern in radial-porous species is similar to that in the d1 type; the pattern in non-vessels species is similar to that in the d2 type. The vessel diameter in radial-porous species is similar to that of the earlywood vessels of semi-ring-porous species. These results suggest that the conduit diameter size is only one of many factors determining the water-conducting pathways of broadleaved evergreen species.

Effect of thinning on the wood structure in annual growth rings of Japanese larch (Larix leptolepis) by

The objective of this study was to determine the effect of thinning on the annual ring structure and the cross-sectional dimensions of tracheids in plantation-grown Japanese larch (Larix leptolepis). Annual ring width, earlywood width and latewood width increased significantly after thinning. The width of the band of nonflat latewood tracheids in the annual ring increased more than that of flat latewood tracheids. Thinning did not significantly affect latewood percentage. The average radial diameter of both earlywood and latewood tracheids increased after thinning. After thinning, average wall thickness of earlywood tracheids increased, while that of latewood tracheids decreased. Cell wall percentage in earlywood was not influenced significantly by thinning, but latewood cell wall percentage decreased. The changes of the average radial tracheid diameter, the average wall thickness of tracheids and cell wall percentage from earlywood to latewood within a growth ring became more gradual after thinning. However, thinning did not affect significantly the cell wall percentage of the whole growth ring. This study suggests that thinning has little effect on wood density of the whole growth ring in Japanese larch.

An application of mixed-effects model to evaluate the effects of initial spacing on radial variation in wood density in Japanese larch (Larix kaempferi )

The effects of initial tree spacing on wood density at breast height were examined for 22-year-old Japanese larch (Larix kaempferi). The experiment involved the use of three plots with different initial tree spacing densities (300, 500, and 1000 trees/ha). For five trees selected from each plot, the total tree height, diameter at breast height, height to the base of the live crown, and crown diameter were measured. Ring width and wood density for individual growth rings were determined by X-ray densitometry. A mixed-effects model was applied for fitting the radial variation in wood density in relation to initial spacing. Models having various mean and covariance structures were tested in devising an appropriate wood density model. The model, consisting of the mean structure with quadratic age effects and heterogeneous first-order autoregressive covariance, was able to describe the radial variation in wood density. Closer spacing of trees (1000 trees/ha) resulted in a faster increase in wood density from the pith outward than for more widely spaced trees, indicating that initial tree spacing may influence the age of transition from juvenile to mature wood.

Termite resistance and color of heartwood of hinoki (Chamaecyparis obtusa) trees in 5 half-sib families in a progeny test stand in Kyushu, Japan

Hinoki (Chamaecyparis obtusa) wood has been used as a structural material in Japan because of its superior mechanical properties, its excellent durability and the beautiful color of its heartwood. Variations of termite resistance and compositions of extractives among hinoki trees have been reported. However, genetic variation of termite resistance and the effect of heartwood color on termite resistance remain unknown. In this study, we report the characteristics of termite resistance and color indexes (L*, a* and b*) of heartwood of hinoki half-sib families in a progeny test stand. The survival days of termites and the mass loss of samples of hinoki heartwood differed significantly among hinoki families. Families with red-color heartwood had larger termite resistance than families with yellow-color heartwood. The termite resistances of individual samples from two families with yellow-color heartwood were as small as that of Pinus densiflora. Larger a* and smaller b* induced larger termite resistance of heartwood. The effect of DBH (diameter at breast height) of hinoki trees on termite resistance of hinoki families was small.

Green moisture content and basic density of 95 woody species growing in Kyushu University Forests, Japan

We investigated the green moisture content and basic density of 95 woody species growing in Kyushu University Forests. In softwood species, the green moisture content of heartwood ranged from 28% in Cryptomeria japonica to 67% in Abies firma, and in sapwood, from 75% in Tsuga sieboldii to 160% in Cryptomeria japonica. The green moisture content of softwood trees was greater in sapwood than heartwood. The green moisture content in the heartwood of hardwood species ranged from 34% in Euonymus alatus f. striatus to 83% in Kalopanax pictus, and in sapwood, from 45% in Fraxinus sieboldiana to 153% in Actinidia polygama. We found three radial variation pattern types in stems of hardwood species. The green moisture content was higher in heartwood than sapwood, in the first type, whereas in the second, it was higher in sapwood than heartwood. In a third type, differences between heartwood and sapwood were relatively small. The basic density of softwood species ranged from 378 kg/m3 in Cryptomeria japonica to 524 kg/m3 in Tsuga sieboldii. Most trees tended to decrease in basic density from corewood to outerwood. Basic density in hardwood species ranged from 266 kg/m3 in Paulownia tomentosa to 751 kg/m3 in Rhaphiolepis indica var. umbellata. We identified three types of radial variation pattern in stems of hardwood species. In the first type, basic density was higher in corewood than outerwood, whereas in second, it was higher in outerwood. In the third type, differences between corewood and outerwood were small. We also provided the information on the age and size of heartwood formation. Keyword:green moisture content; basic density; Kyushu University Forests; Japan

The effect of bark decortication for hiwada production on xylem and phloem formation in Chamaecyparis obtusa

Of all plant materials used to cover the roofs of traditional Japanese buildings, Japanese cypress (Chamaecyparis obtusa) bark, hiwada, has the longest service life and has been used from ancient times. However, wood and bark properties after hiwada harvest have not been evaluated in detail. We studied whether decortication for hiwada production in winter affected xylem and phloem formation. Decorticated trees still preserved all inner bark and part of the outer bark, and both decorticated and control trees had similar annual ring structures at all stem heights in the xylem and phloem. In both xylem and inner bark, no significant difference in ring width at any stem height was found between annual rings before and after decortication. Thus, this study revealed that the decortication of bark for hiwada production does not affect the formation of xylem and the inner and outer bark if decortication is carried out by highly skilled workers in winter.

Effects of application of trans -zeatin on tracheid differentiation in mature sugi ( Cryptomeria japonica ) trees

The mechanism of differentiation of tracheid (earlywood or latewood) should be elucidated to improve the wood properties of sugi trees (Cryptomeria japonica). Water deficit affects tracheid differentiation in conifers. However, the signals, which transmit the information of water contents in the soil to the differentiating tracheid, remain unknown. Plant responses with deficits of macronutrients or water showed some differences but also similarities, mostly involving hormonal long-distance signaling. In Arabidopsis, trans-zeatin (tZ)-type cytokinins play a role as a root-to-shoot acropetal signal. In this study, we report the effects of applying tZ alone or in combination with other phytohormones on tracheid differentiation in mature sugi trees forming latewood. The application of tZ induced the formation of earlywood-type tracheids with significantly smaller cell wall ratios and larger microfibril angles than those of controls in July, August and September. The application of indole acetic acid (IAA) in combination with tZ inhibited the effects of applied tZ, although gibberellic acid (GA3) did not. In October and November, application of tZ could not affect the xylem formation or dormancy of cambium. We hypothesized that tZ might play a role in the differentiation of earlywood tracheid.